have you tried testing the coil packs? these are the bits that are on top of your spark plugs instead of normal HT leads.
they are prone to faults and about £130 each to replace!
my car had the same symptoms, starting with a mild misfire and then shuddering and stalling when coming to junctions etc.
ask your local dealer to test them for you as the timing chain is not likely to be your problem.
my car had done 40,000 miles when this occurred at 5 years old.
paul
October 2009